Promiscuous birds hatch more dud chicks, according to new findings, which counter existing ideas about the evolution of promiscuity.
Dr Jane Reid and Dr Rebecca Sardell from the University of Aberdeen report in the Proceedings of the Royal Society Bthat when promiscuous song sparrows mate with birds other than their partner, these couplings produce worse quality offspring.
Many female birds are promiscuous and it’s generally been assumed that this is because they can get better quality genes from a stranger than from their partner.
However, Reid and Sardell found that song sparrow chicks sired by non-partner males actually had slightly less chance of surviving to breeding age (about 2 per cent less) than chicks fathered by their mother’s regular partner.
They also used a method called quantitative genetics to determine that non-partner males were less genetically fit than the female’s regular partner.
The study looked at breeding behaviour in an isolated population of song sparrows living in grasslands on the island of Mandarte, off the coast of Canada.
Although these birds team up with a single mate for one or even several years, previous genetic studies have shown that about 26 per cent of chicks are sired by a male other than the female’s partner.